Something weird has happened all of a sudden: My ESP32 board has stopped working after being used only once. The board is recognized by the PC. However when I try programming, I get "error: espcomm_upload_mem failed".I have tried numerous things but nothing has worked.Does someone have an idea on what to do and how to fix this issue?

I've not heard of this before from a customer but there's a first time for everything. There are two devices involved in communication between the programming environment and the ESP32. They are the ESP32 and the USB to Serial converter and potentially the 3.3V LDO that powers the ESP32. If the LDO is dead or damaged then the 3.3V output on the pins won't be at 3.3V. Please check that you find the correct voltage on one of the pins marked as a 3.3V pin.

Since the PC recognizes the board, the USB to Serial converter is almost certainly good so I'm going to assume that the problem is elsewhere. It is possible for the PC to recognize the board even if the ESP32 is entirely absent because the USB interface is powered from the USB cable.

The next possibility is a timing issue with the downloader. There are a few ways to generate timing troubles. One is with marginal USB cables. An easy way to verify that timing is not an issue is to drop the upload speed to 115200bps. If the board works then we can go from there.

The other possibility is that you programmed the board to go to sleep after a short time of doing something. This may cause the board to appear to be dead. The sequence goes like this: The downloader resets the board. The board resets, runs the user code and goes to sleep. Unless the timing of the bootloader is perfect the board appears to be dead. I've had this resolved by trying many downloads to get one to work. PlatformIO is a much better route for doing this since it doesn't recompile the code before every download attempt.

The last option is to slow down the reset signal by soldering a 10uF cap from Reset to ground. That has been 100% successful for me.

Let me know if you are still stuck after trying these suggestions.Daniel